Recently, there has been rapidly spread an optical disk device capable of recording and reproducing both sides of a disk which has a plurality of standards of DVD/CD having different substrate thickness. However, in the DVD/CD standard disks, since laser wavelengths and detection methods of tracking/focus errors are different, it may be necessary to previously determine the kind of DVD/CD in the optical disk device. FIGS. 13A to 13C are cross-sectional views showing a structure of the DVD/CD standard disk. FIG. 13A shows a structure of a CD, FIG. 13B shows a structure of a DVD having single side and single layer, and FIG. 13C shows a structure of a DVD having single side and double layers. All disks have a same entire thickness of 1.2 mm.
In the CD shown in FIG. 13A, reference numeral 100 represents a disk surface, reference numeral 101 represents a disk substrate formed of a transparent layer, reference numeral 102 represents a signal surface, reference numeral 103 represents a reflective layer, and reference numeral 104 represents a protective layer. In the DVD having single side and single layer shown in FIG. 13B, reference numeral 120 represents the disk surface, reference numeral 121 represents the disk substrate formed of the transparent layer, reference numeral 122 is the signal surface, reference numeral 123 represents the reflective surface, reference numeral 126 is an adhesive surface, and reference numeral 127 is a dummy plate. In the DVD having single side and double layers shown in FIG. 13C, reference numeral 130 represents the disk surface, reference numeral 131 is the disk substrate formed of the transparent layer, reference numeral 132 represents a first signal surface, reference numeral 133 represents a first reflective surface, reference numeral 134 represents a second signal surface, reference numeral 135 represents a second reflective surface, reference numeral 136 represents the adhesive surface, and reference numeral 137 represents the dummy plate.
In the above-mentioned respective kinds of disks, the thicknesses of the signal surface, the reflective layer, and the protective layer are actually much smaller than those of the disk substrates 101, 121, and 131, respectively. In the CD shown in FIG. 13A, the thickness of the disk substrate 101 from the disk surface 100 to the signal surface 102 is about 1.2 mm and is approximately the same as the disk thickness. In the DVD having the one single-sided layer shown in FIG. 13B and the DVD having single side and double layers shown in FIG. 13C, the disk thickness of the disk substrates 121 and 131 from the disk surfaces 120 and 130 to the signal surface 122 and the first signal surface 132 is 0.6 mm and is approximately the same as ½ of the disk thickness. The following technique is proposed as a determination method for a plurality of kinds of disks having different substrate thickness.
In an optical disk device disclosed in JP-A-9-259511, a discrimination sensor includes a first light emitting unit which emits a diffusion light having 700 nm or lower and a second light emitting unit which emits a diffusion light of 800 nm or higher, and a light receiving unit disposed between the first light emitting unit and the second light emitting unit, which receives a reflective light reflected in a recording layer of the optical disk. The first light emitting unit and the second light emitting unit alternatively emit light by an LED driving unit. A CPU discriminates the kind of the disks depending on a reflected light amount received by the light receiving unit.
A disk detection mechanism disclosed in JP-A-8-335361 includes mounting means supported to be inserted into and discharged from an optical disk player body, which can rotatably mount or dismount the optical disk having the signal recording surface and the protective layer provided on an upper layer of the signal recording surface; a light emitting element disposed opposite to the signal recording surface of the optical disk mounted by the mounting means, which radiates a laser beam to the signal recording surface; a light receiving element which receives the reflective light from the optical disk; and detection means which detects through the light receiving element a difference of the reflected light amount from the optical disks caused by a difference in thickness-direction position between the signal recording surface of the optical disk and the disk surface. Accordingly, by differentiating a light reaching distance on the light receiving surface by the difference in thickness-direction position between the signal recording surface and the disk surface, that is, the difference in thickness of the protection layer, it is possible to easily determine the kind of the disks.
An optical disk device disclosed in JP-A-9-91858 includes a focus serve system which constantly keeps an objective lens in on-focus state. In the focus servo system, when the objective lens is kept in the on-focus state, a DC offset voltage is applied to a coil driving the objective lens from a drive circuit. Since optical disks having different recording density have transparent disk substrates having different thickness, DC offset voltage, which makes the objective lens kept in the on-focus state, is different respectively. Accordingly, it is possible to specify the position of the objective lens, that is, the kind of the optical disks by detecting the DC offset voltage. That is, the method is a method of determining the kind of the disks by detecting an absolute position of the signal surface by the DC offset voltage during the on-focus state and indirectly calculating a distance from the disk surface to the signal surface, assumed that a distance to a turntable which lays the optical disk from an optical pickup is substantially the same as a distance to the disk surface from the optical pickup.